According to Documentation/Changes, the kernel should be buildable with
GNU make 3.80+. Commit 88d7be031f9f975bb3f50a0b5ef3796a671e7edf (kbuild:
Use a single clean rule for kernel and external modules) introduced the
"$(or" construct, which requires make 3.81. This causes "make clean" to
malfunction when it is used with external modules.